1. Field of the Invention
This invention relates to electrodeless lamps, and, in particular, to electrodeless lamps having a fill including a rare earth constituent. Accordingly, it is a general object of this invention to provide new and improved lamps of such character.
2. Description of the Prior Art
High pressure electric discharge lamps of the electroded type containing mercury and metal iodides such as scandium iodide and sodium iodide provide high efficacy (about 100 lpW), but only fair color rendering (CRI.apprxeq.65). In response to the need for high color rendering, tin halide lamps have been developed, in which the molecular continuum from the tin halide provides excellent color rendering, but only fair efficacy (about 60 lpW). However, the tin chloride used in such lamps tended to attack the tungsten electrodes, presenting a lifetime problem. In response to a need for a high efficacy and a high color rendering index for applications such as studio lighting, rare-earth halide fill lamps have been developed. The emission spectra of the rare-earth atoms provide many lines throughout the visible range. However, in order to get the rare-earth halide fills into the discharge, very high wall loadings are required, resulting in a rapid decrease in color temperature (about 1.degree. K/hour) and a very short effective lifetime of about 200 hours.
A rare-earth halide electroded studio lamp having a fill consisting of mercury, dysprosium iodide, holmium iodide, cesium iodide, mercuric bromide, and argon (Hg/DyI.sub.3 /CsI/HgBr.sub.2 /Ar) is commercially available. Thus, the use of a rare-earth halide in electroded studio lamps is known.
One example of an electroded lamp filled with mercury and argon, and iodides of dysprosium, holmium and thulium, developed by OSRAM GmbH, Germany is discussed in an article entitled "A New Daylight Light Source" by Werner Block, Michael J. McGovern, and Thomas M. Lemons, September 1974, Journal of the SMPTE, Volume 83, pages 725-6.
Electrodeless lamps, per se, are known. For example, the following United States Patents, which may be of interest, relate to electrodeless lamps, usually at least one of the patentees of each patent is an applicant of this application, and all patents have been assigned to a common assignee.
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 3,942,058 Haugsjaa et al. March 2, 1976 3,942,068 Haugsjaa et al. March 2, 1976 3,943,401 Haugsjaa et al. March 9, 1976 3,943,402 Haugsjaa et al. March 9, 1976 3,943,403 Haugsjaa et al. March 9, 1976 3,943,404 McNeill et al. March 9, 1976 3,993,927 Haugsjaa et al. November 23, 1976 3,995,195 Haugsjaa et al. November 30, 1976 3,997,816 Haugsjaa et al. December 14, 1976 4,001,631 McNeill et al. January 4, 1977 4,001,632 Haugsjaa et al. January 4, 1977 4,002,943 Regan et al. January 11, 1977 4,002,944 McNeill et al. January 11, 1977 4,041,352 McNeill et al. August 9, 1977 4,053,814 Regan et al. October 11, 1977 4,065,701 Haugsjaa et al. December 27, 1977 4,070,603 Regan et al. January 24, 1978 ______________________________________
Also of interest is the following U.S. patent which relates to electrodeless lamps. U.S. Pat. No. 3,787,705, Bolin et al. Jan. 22, 1974.